Naked Single
nakedSingle
LevelNot seen in a hint yet
How it works
Take one cell and strike out every digit already present in its row, column and box. Sometimes exactly one digit survives. Nothing further needs checking — that digit is confirmed.
The candidate is naked: you can read it off the single cell without looking anywhere else. Striking out eight to leave one is the most basic move there is, and it is also what finishes the job after another technique has cleared candidates away.
Worked example
1
7
6
3
8
5
8
2
1
6
5
6
8
1
9
2
5
4
9
3
1
7
8
6
1
7
8
6
4
7
6
8
5
9
1
3
5
1
9
4
3
7
2
8
7
9
1
6
3
7
1
9
2
5
8
4
● evidence✕ eliminated★ confirmed
Look at the row, column and box that R4C7 belongs to.
That scope already contains 1, 2, 3, 4, 5, 6, 8, 9 (marked ●), so none of those digits can go in this cell.
Only 7 remains — R4C7 takes 7 (★).
Examples I encountered
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